Signaling for non-merge inter modes

ABSTRACT

Aspects of the disclosure provide methods and apparatuses for video encoding/decoding. In some examples, an apparatus for video decoding includes receiving circuitry and processing circuitry. The processing circuitry decodes prediction information of a current block from a coded video bitstream. The prediction information is indicative of a subset of inter prediction modes associated with a merge flag being false. Then, the processing circuitry decodes at least an additional flag that is used for selecting a specific inter prediction mode from the subset of inter prediction modes. Further, the processing circuitry reconstructs samples of the current block according to the specific inter prediction mode.

INCORPORATION BY REFERENCE

This application is a Continuation of U.S. patent application Ser. No.16/733,038, filed Jan. 2, 2020, which claims the benefit of priority toU.S. Provisional Application No. 62/788,835, “SIGNALING FOR NON-MERGEINTER MODES” filed on Jan. 5, 2019, wherein the entire content anddisclosure of each of which is incorporated by reference herein in itsentirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 1 , a current block (101) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2. (102 through 106, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes receiving circuitry and processing circuitry. The processingcircuitry decodes prediction information of a current block from a codedvideo bitstream. The prediction information is indicative of a subset ofinter prediction modes associated with a merge flag being false. Then,the processing circuitry decodes at least an additional flag that isused for selecting a specific inter prediction mode from the subset ofinter prediction modes. Further, the processing circuitry reconstructssamples of the current block according to the specific inter predictionmode.

In some examples, the subset of inter prediction modes includes at leastone of merge with motion vector difference (MMVD) inter prediction mode,subblock based temporal motion vector predictor (SbTMVP) predictionmode, combined inter and intra prediction (CIIP) inter prediction mode,triangle inter prediction mode, affine merge inter prediction mode,advanced motion vector predictor (AMVP) inter prediction mode, andaffine AMVP inter prediction mode.

In some embodiments, each of the inter prediction modes in the subsetuses a motion vector difference in prediction. In an example, advancedmotion vector predictor (AMVP) inter prediction mode is not in thesubset. In another example, advanced motion vector predictor (AMVP)inter prediction mode is in the subset.

In an embodiment, the processing circuitry decodes, when a first flag isindicative of an affine mode, a second flag that is used to select onefrom an affine merge inter prediction mode and an affine advanced motionvector predictor (AMVP) inter prediction mode.

In another embodiment, the processing circuitry decodes flagsrespectively corresponding to the inter prediction modes in the subsetto select the specific inter prediction mode.

In an example, the processing circuitry decodes flags respectivelycorresponding to the inter prediction modes in the subset that areordered before a last one in the subset, and selects the last one whenthe flags are false.

In another example, the processing circuitry decodes an index that isindicative of the specific inter prediction mode from the interprediction modes in the subset.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system (200) in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 8 shows a diagram illustrating redundancy check pairs for someembodiments.

FIG. 9 shows an example for temporal candidate derivation.

FIG. 10 shows an example for illustrating the position for the temporalcandidate.

FIG. 11 shows examples for merge mode with motion vector difference(MMVD) according to an embodiment of the disclosure.

FIGS. 12A-12B show the affine motion field of a block described bymotion information of control points.

FIG. 13 shows an example of affine motion vector field per sub-block.

FIG. 14 shows an example for affine merge mode.

FIG. 15 shows an example of spatial neighbors and temporal neighboraccording to some embodiments of the disclosure.

FIG. 16 shows an example of spatial neighbors according to someembodiments of the disclosure.

FIG. 17 shows an example of a SbTVMP process according to someembodiments of the disclosure.

FIG. 18 shows examples of triangular partition.

FIG. 19 shows an example for forming a uni-prediction candidate list fora current block.

FIG. 20 shows an example of using weighting factor group to derive thefinal prediction according to some embodiments of the disclosure.

FIG. 21 shows another example of using weighting factor group to derivethe final prediction according to some embodiments of the disclosure

FIG. 22 shows examples of prediction for triangular partition.

FIG. 23 shows a flow chart outlining a process example according to someembodiments of the disclosure.

FIG. 24 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data, transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313), that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4 . The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values, thatcan be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (452) has generated to the outputsample information as provided by the scaler/inverse transform unit(451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec., H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) transmitting circuitry). The video encoder(503) can be used in the place of the video encoder (303) in the FIG. 3example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4 . Brieflyreferring also to FIG. 4 , however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415), andparser (420) may not be fully implemented in the local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction of intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6 .

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) of the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7 .

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (503), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

Aspects of the disclosure provide signaling techniques for non-mergeinter modes in advanced video codec. To be more specific, theinterpretation and signaling of implicitly derived motion vectorpredictors are modified so that better compression efficiency may beachieved.

Various coding standards, such as HEVC, VVC and the like are developedto include new techniques.

In some examples of VVC, for each inter-predicted CU, motion parametersinclude motion vectors, reference picture indices and reference picturelist usage index, and additional information needed for the new codingfeature of VVC to be used for inter-predicted sample generation. Themotion parameters can be signaled in an explicit or implicit manner. Inan example, when a CU is coded with skip mode, the CU is associated withone PU and has no significant residual coefficients, no coded motionvector delta or reference picture index. In another example, a mergemode is specified whereby the motion parameters for the current CU areobtained from neighboring CUs, including spatial and temporalcandidates, and additional schedules introduced in VVC. The merge modecan be applied to any inter-predicted CU, not only for skip mode. Thealternative to merge mode is the explicit transmission of motionparameters, where motion vector, corresponding reference picture indexfor each reference picture list and reference picture list usage flagand other needed information are signaled explicitly per each CU.

Beyond the inter coding features in HEVC, the VVC test model 3 (VTM3)includes a number of new and refined inter prediction coding tools, suchas extended merge prediction, merge mode with motion vector difference(MMVD), affine motion compensated prediction, subblock-based temporalmotion vector predictor (SbTMVP), triangle partition prediction,combined inter and intra prediction (CIIP), and the like. Some featuresof the above mentioned inter prediction coding tools are described inthe present disclosure.

In some examples, extended merge prediction is used in VTM3.Specifically, in In VTM3, the merge candidate list is constructed byincluding, the five types of candidates in an order of (1) spatialmotion vector predictor (MVP) from spatial neighbor CUs; (2) temporalMVP from collocated CUs; (3) history-based MVP from a FIFO table; (4)pairwise average MVP; and (5) zero MVs. In some embodiments, thetechniques used in merge candidate list construction include spatialcandidate derivation, temporal candidates derivation, history-basedmerge candidates derivation and pair-wise average merge candidatesderivation.

In an example, the size of merge list is signaled in slice header andthe maximum allowed size of a merge list is 6 in VTM3. For each CU codedin merge mode, an index of the best merge candidate is encoded usingtruncated unary binarization (TU). The first binary of the merge indexis coded with context coding, and bypass coding can be used for otherbinaries.

For spatial candidate derivation, according to an aspect of thedisclosure, the derivation of spatial merge candidates in VVC is similarto that in HEVC. For example, a maximum of four merge candidates areselected among candidates located in the positions A0-A1 and B0-B1depicted in FIG. 1 . The order of derivation is A1, B1, B0, A0 and B2.Position B2 is considered only when any CU of position A1, B1, B0, A0 isnot available (e.g. belonging to another slice or tile) or is intracoded. After candidate at position A1 is added, the addition of theremaining candidates is subject to a redundancy check which ensures thatcandidates with same motion information are excluded from the list sothat coding efficiency is improved. To reduce computational complexity,not all possible candidate pairs are considered in the mentionedredundancy check. Instead only the pairs linked with an arrow in FIG. 8are considered and a candidate is only added to the list if thecorresponding candidate used for redundancy check has not the samemotion information.

For temporal candidate derivation, according to an aspect of thedisclosure, only one candidate is added to the list. Particularly, inthe derivation of the temporal merge candidate, a scaled motion vectoris derived based on a co-located CU belonging to the collocatedreference picture. The reference picture list to be used for derivationof the co-located CU is explicitly signaled in the slice header.

FIG. 9 shows an example for temporal candidate derivation. FIG. 9 showsa sequence of pictures that includes a current picture having a currentCU, a collocated picture having a col-located CU of the current CU, areference picture of the current picture and a reference picture of thecol-located picture. In an example, a picture order count (POC) distance(e.g., difference of POCs) between the reference picture of the currentpicture and the current picture is denoted as tb, and the POC distancebetween the reference picture of the col-located picture and thecol-located picture is denoted as td. The scaled motion vector fortemporal merge candidate is shown by 910 in FIG. 9 , which is scaledfrom the motion vector 920 of the co-located CU using the POC distances,tb and td. The reference picture index of temporal merge candidate isset equal to zero.

FIG. 10 shows an example for illustrating the position for the temporalcandidate that is selected between candidates C₀ and C₁. When the CU atposition C₀ is not available, or is intra coded, or is outside of thecurrent row of CTUs, then the position C₁ can be used. Otherwise, theposition C₀ is used in the derivation of the temporal merge candidate.

The history-based MVP (HMVP) merge candidates are added to merge listafter the spatial MVP and temporal MVP (TMVP). In some examples, forhistory-based merge candidate derivation, the motion information of apreviously coded block is stored in a table and used as MVP for thecurrent CU. The table with multiple HMVP candidates is maintained duringthe encoding/decoding process. The table is reset (emptied) when adecoding of a new CTU row starts. Whenever there is a non-subblockinter-coded CU, the associated motion information is added to the lastentry of the table as a new HMVP candidate.

In some examples, such as in VTM3, the HMVP table size S is set to be 6,which indicates up to 6 history-based MVP (HMVP) candidates may be addedto the table. At a time of inserting a new motion candidate to thetable, a constrained first-in-first-out (FIFO) rule is utilized whereinredundancy check is firstly applied to find whether there is anidentical HMVP in the table. If an identical HMVP in the table is found,the identical HMVP is removed from the table and all the HMVP candidatesafterwards can move forward.

HMVP candidates can be used in the merge candidate list constructionprocess. The latest several HMVP candidates in the table are checked inorder and inserted to the candidate list after the TMVP candidate.Redundancy check is applied on the HMVP candidates to the spatial ortemporal merge candidate.

In some examples, to reduce the number of redundancy check operations,some simplifications are introduced. In an example, the number of HMPVcandidates is used for merge list generation is set as (N<=4) ? M:(8−N), where N denotes the number of existing candidates in the mergelist and M denotes the number of available HMVP candidates in the table.

In another example, once the total number of available merge candidatesis 1 below the maximum value for the allowed merge candidates, the mergecandidate list construction process from HMVP is terminated.

For the pair-wise average merge candidates derivation, pair-wise averagecandidates are generated by averaging predefined pairs of candidates inthe existing merge candidate list. In some examples, the predefinedpairs are defined as {(0, 1), (0, 2), (1, 2), (0, 3), (1, 3), (2, 3)},where the numbers denote the merge indices in the merge candidate list.The averaged motion vectors are calculated separately for each referencelist. When both motion vectors are available in one reference list,these two motion vectors are averaged even when they point to differentreference pictures. When only one motion vector is available inreference list, use the one motion vector directly; if no motion vectoris available in the reference list, the reference list is invalid.

In some examples, when the merge list is not full after pair-wiseaverage merge candidates are added, the zero MVPs are inserted in theend until the maximum merge candidate number is encountered.

In addition to merge mode, where the implicitly derived motioninformation is directly used for prediction samples generation of thecurrent CU, the merge mode with motion vector differences (MMVD) isintroduced in VVC. In some examples, a MMVD flag is signaled right aftersending a skip flag and a merge flag to specify whether MMVD mode isused for a CU.

In MMVD, after a merge candidate is selected, the motion information isfurther refined by the signaled motion vector difference (MVD)information. In some examples, the information includes a mergecandidate flag, an index to specify motion magnitude, and an index forindication of motion direction. In MMVD mode, one of the first twocandidates in the merge list is selected to be used as MV basis. Themerge candidate flag is signaled to specify which one is used.

In some examples, a distance index is used to specify motion magnitudeinformation and indicate the pre-defined offset from a starting point.

FIG. 11 shows examples for MMVD according to an embodiment of thedisclosure. For example, the starting point MV is shown by (1111) (forexample according to a prediction direction IDX and base candidate IDX).The offset is added to either horizontal component or vertical componentof starting MV. An example of the relation of distance index andpre-defined offset is shown in Table 1.

TABLE 1 Relation of distance index and pre-defined offset Distance MX 01 2 3 4 5 6 7 Offset (in unit of 1/4 1/2 1 2 4 8 16 32 luma sample)

In some examples, direction index represents the direction of the MVDrelative to the starting point. The direction index can represent of thefour directions as shown in Table 2. It's noted that the meaning of MVDsign could be variant according to the information of starting MVs. Whenthe starting MVs is an uni-prediction MV or bi-prediction MVs with bothlists point to the same side of the current picture (i.e. POCs of tworeference pictures are both larger than the POC of the current picture,or are both smaller than the POC of the current picture), the sign inTable 2 specifies the sign of MV offset added to the starting MV. Whenthe starting MVs is bi-prediction MVs with the two MVs point to thedifferent sides of the current picture (i.e. the POC of one referencepicture is larger than the POC of the current picture, and the POC ofthe other reference picture is smaller than the POC of the currentpicture), the sign in Table 2 specifies the sign of MV offset added tothe list0 MV component of starting MV and the sign for the list1 MV hasopposite value.

TABLE 2 Sign of MV offset specified by direction index Direction IDX 0001 10 11 x-axis + − N/A N/A y-axis N/A N/A + −

For affine motion compensated prediction, in HEVC, only translationmotion model is applied for motion compensation prediction (MCP). Thereal world has many kinds of motion, e.g. zoom in/out, rotation,perspective motions and the other irregular motions. In the VTM3, ablock-based affine transform motion compensation prediction is applied.

FIG. 12A shows the affine motion field of the block that is described bymotion information of two control points (4-parameter affine model) andFIG. 12B shows the affine motion field of a block that is described bythree control points (6-parameter affine model).

In some embodiments, the 4-parameter affine motion model, motion vectorat sample location (x, y) in a block can be derived as Eq. 1, and the6-parameter affine motion model, motion vector at sample location (x, y)in a block can be derived as Eq. 2:

$\begin{matrix}\left\{ \begin{matrix}{{mv}_{x} = {{\frac{{mv}_{1x} - {mv}_{0x}}{W}x} + {\frac{{mv}_{1y} - {mv}_{0y}}{W}y} + {mv}_{0x}}} \\{{mv}_{y} = {{\frac{{mv}_{1y} - {mv}_{0y}}{W}x} + {\frac{{mv}_{1y} - {mv}_{0x}}{W}y} + {mv}_{0y}}}\end{matrix} \right. & \left( {{Eq}.\mspace{14mu} 1} \right) \\\left\{ \begin{matrix}{{mv}_{x} = {{\frac{{mv}_{1x} - {mv}_{0x}}{W}x} + {\frac{{mv}_{2x} - {mv}_{0x}}{H}y} + {mv}_{0x}}} \\{{mv}_{y} = {{\frac{{mv}_{1y} - {mv}_{0y}}{W}x} + {\frac{{mv}_{2y} - {mv}_{0y}}{H}y} + {mv}_{0y}}}\end{matrix} \right. & \left( {{Eq}.\mspace{14mu} 2} \right)\end{matrix}$where (mv_(0x), mv_(0y)) denotes the motion vector of the top-leftcorner control point CP0, (mv_(1x), mv_(1y)) is motion vector of thetop-right corner control point CP1, and (mv_(2x), mv_(2y)) is motionvector of the bottom-left corner control point CP2.

In order to simplify the motion compensation prediction, block basedaffine transform prediction is applied.

FIG. 13 shows an example of affine MV field per sub-block. The currentCU is divided into 4×4 luma sub-blocks. To derive motion vector of each4×4 luma sub-block, the motion vector of the center sample of eachsub-block, as shown in FIG. 13 , is calculated according to aboveequations, and rounded to 1/16 fraction accuracy. Then the motioncompensation interpolation filters are applied to generate theprediction of each sub-block with derived motion vector. The sub-blocksize of chroma-components is also set to be 4×4. The MV of a 4×4 chromasub-block is calculated as the average of the MVs of the fourcorresponding 4×4 luma sub-blocks in an example.

Two affine motion inter prediction modes, such as affine merge(AF_MERGE) mode and affine advanced MVP (AMVP) mode, can be used.

For affine merge prediction, in an example, AF_MERGE mode can be appliedfor CUs with both width and height larger than or equal to 8. In theAF_MERGE mode, the control point motion vectors (CPMVs) of the currentCU are generated based on the motion information of the spatialneighboring CUs. In an example, there can be up to five CPMVP candidatesand an index is signalled to indicate the one to be used for the currentCU. In an example, three types of CPVM candidates are used to form theaffine merge candidate list. The first type of CPMV candidates isinherited affine merge candidates that extrapolated from the CPMVs ofthe neighbour CUs. The second type of CPMV candidates are constructedaffine merge candidates CPMVPs that are derived using the translationalMVs of the neighbour CUs. The third type of CPMV candidates is Zero MVs.

In some examples, such as in VTM3, a maximum of two inherited affinecandidates can be used. In an example, two inherited affine candidatesare derived from affine motion models of the neighboring blocks, onefrom left neighboring CUs (referred to as left predictor) and one fromabove neighboring CUs (referred to as above predictor). In someexamples, for the left predictor, the scan order is A0→A1, and for theabove predictor, the scan order is B0→B1→B2. In an example, only thefirst inherited candidate from each side is selected. In some examples,no pruning check is performed between two inherited candidates. When aneighboring affine CU is identified, the control point motion vectors ofthe neighboring affine CU are used to derive the CPMVP candidate in theaffine merge list of the current CU.

FIG. 14 shows an example for affine merge mode. As shown in FIG. 14 ,when the neighbour left bottom block A is coded in affine mode, themotion vectors mv₂, mv₃ and mv₄ of the top left corner, above rightcorner and left bottom corner of a CU which contains the block A areattained. When block A is coded with 4-parameter affine model, the twoCPMVs of the current CU are calculated according to mv₂, and mv₃. Incase that block A is coded with 6-parameter affine model, the threeCPMVs of the current CU are calculated according to v₂, mv₃ and mv₄.

In some examples, a constructed affine candidate is constructed bycombining the neighbor translational motion information of each controlpoint. The motion information for the control points can be derived fromthe specified spatial neighbors and temporal neighbor.

FIG. 15 shows an example of spatial neighbors (e.g., A0-A2 and B0-B3)and temporal neighbor (e.g., T) according to some embodiments of thedisclosure. In an example, CPMV_(k)(k=1, 2, 3, 4) represents the k-thcontrol point. For CPMV₁, the B2→B3→A2 blocks are checked (→ is used forchecking order) and the MV of the first available block is used. ForCPMV₂, the B1→B0 blocks are checked and for CPMV₃, the A1→A0 blocks arechecked. For TMVP, T is checked and is used as CPMV₄ if the MV of theblock T is available.

After MVs of four control points are attained, affine merge candidatesare constructed based on that motion information. The followingcombinations of control point MVs are used to construct in order:{CPMV₁, CPMV₂, CPMV₃}, {CPMV₁, CPMV₂, CPMV₄}, {CPMV₁, CPMV₃, CPMV₄},{CPMV₂, CPMV₃, CPMV₄}, {CPMV₁, CPMV₂}, {CPMV₁, CPMV₃}.

The combination of 3 CPMVs can construct a 6-parameter affine mergecandidate and the combination of 2 CPMVs can construct a 4-parameteraffine merge candidate. In an example, to avoid motion scaling process,when the reference indices of control points are different, the relatedcombination of control point MVs can be discarded.

In an example, after inherited affine merge candidates and constructedaffine merge candidate are checked, if a candidate list is still notfull, zero MVs are inserted to the end of the list.

For affine AMVP prediction, the affine AMVP mode can be applied on CUswith both width and height larger than or equal to 16. In some examples,affine flag at CU level is signalled in the bitstream. (e.g., codedvideo bitstream) to indicate whether affine AMVP mode is used in the CUand then another flag is signaled to indicate whether 4-parameter affineor 6-parameter affine is used. In the affine AMVP mode, the differenceof the CPMVs of current CU and their predictors CPMVPs is signalled inthe bitstream. The affine AMVP candidate list size is 2 and the affineAMVP candidate list is generated by using the following four types ofCPVM candidate in the order: (1) inherited affine AMVP candidates thatextrapolated from the CPMVs of the neighbour CUs; (2) constructed affineAMVP candidates CPMVPs that are derived using the translational MVs ofthe neighbour CUs; (3) translational MVs from neighboring CUs; and (4)Zero MVs.

In some examples, the checking order of inherited affine AMVP candidatesis the same as the checking order of inherited affine merge candidates.In an example, the only difference between the affine merge predictionand affine AMVP prediction is that, for AMVP candidate, only the affineCU that has the same reference picture as the current block isconsidered. In an example, no pruning process is applied when insertingan inherited affine motion predictor into the candidate list.

In some examples, constructed AMVP candidate can be derived from thespecified spatial neighbors shown in FIG. 15 . In an example, the samechecking order is used as done in the candidate construction for theaffine merge prediction. In addition, reference picture index of theneighboring block is also checked. The first block in the checking orderthat is inter coded and has the same reference picture as in current CUsis used. When the current CU is coded with 4-parameter affine mode, andmotion vectors of two control points mv₀ and mv₁ are both available, themotion vectors of the two control points are added as one candidate inthe affine AMVP list. When the current CU is coded with 6-parameteraffine mode, and all three motion vectors of the control points CPMVsare available, they are added as one candidate in the affine AMVP list.Otherwise, constructed AMVP candidate is set as unavailable.

When the number of affine AMVP list candidates is still less than 2after inherited affine AMVP candidates and constructed AMVP candidateare checked, mv₀, mv₁ and mv₂ will be added, in order, as thetranslational MVs to predict all control point MVs of the current CU,when available. Finally, zero MVs are used to fill the affine AMVP listif the affine AMVP list is still not full.

In some examples, the subblock-based temporal motion vector prediction(SbTMVP) can be used in VTM. Similar to the temporal motion vectorprediction (TMVP) in HEVC, SbTMVP uses the motion field in thecollocated picture to improve motion vector prediction and merge modefor CUs in the current picture. In some examples, the same collocatedpicture used by TMVP is used for SbTVMP. SbTMVP differs from TMVP in twoaspects. In the first aspect, TMVP predicts motion at CU level butSbTMVP predicts motion at sub-CU level. In the second aspect, TMVPfetches the temporal motion vectors from the collocated block in thecollocated picture (the collocated block is the bottom-right or centerblock relative to the current CU), SbTMVP applies a motion shift beforefetching the temporal motion information from the collocated picture.The motion shift is obtained from the motion vector from one of thespatial neighboring, blocks of the current CU.

FIGS. 16-17 show an example of a SbTVMP process according to someembodiments of the disclosure. SbTMVP predicts the motion vectors of thesub-CUs within the current CU in two steps. In the first step, thespatial neighbors shown in FIG. 16 are examined in the order of A1, B1,B0 and A0 to identify a first spatial neighboring block that has amotion vector using the collocated picture as its reference picture.Then, the motion vector using the collected picture as its referencepicture is selected to be the motion shift to be applied. If no suchmotion is identified from the spatial neighbors of A1, B1, B0, and A0,then the motion shift is set to (0, 0).

In the second step, the motion shift identified in the first step isapplied (i.e. added to the current block's coordinates) to obtainsub-CU-level motion information (motion vectors and reference indices)from the collocated picture as shown in FIG. 17 . In the FIG. 17example, A1's motion vector is set as the motion shift (1710). Then, foreach sub-CU, the motion information of the corresponding block (thesmallest motion grid that covers the center sample) in the collocatedpicture is used to derive the motion information for the sub-CU. Afterthe motion information of the collocated sub-CU is identified, it isconverted to the motion vectors and reference indices of the currentsub-CU in a similar way as the TMVP process of HEVC. For example,temporal motion scaling is applied to align the reference pictures ofthe temporal motion vectors to those of the current CU.

In some examples, such as in VTM3, a combined sub-block based merge listwhich includes both SbTVMP candidate and affine merge candidates is usedfor the signalling of sub-block based merge mode. The SbTVMP mode isenabled/disabled by a sequence parameter set (SPS) flag. When the SbTMVPmode is enabled, the SbTMVP predictor is added as the first entry of thecombined sub-block based merge list, and followed by the affine mergecandidates. The maximum allowed size of the sub-block based merge listis 5 in VTM3.

In an example, the sub-CU size used in SbTMVP is fixed to be 8×8, and asdone for affine merge mode, SbTMVP mode is only applicable to the CUwith both width and height are larger than or equal to 8.

In some embodiments, the encoding logic of the additional SbTMVP mergecandidate is the same as for the other merge candidates. In an example,for each CU in P or B slice, an additional rate distortion check isperformed to decide whether to use the SbTMVP candidate.

In some examples, triangular prediction is used in VTM3 for interprediction. The mode that uses the triangular prediction is referred toas triangle partition mode. In some examples, the triangle partitionmode is only applied to CUs that satisfies certain conditions, such ashave a size of 8×8 or larger and are coded in skip or merge mode. For aCU that satisfies these conditions, a CU-level flag is signaled toindicate whether the triangle partition mode is applied or not.

When the triangle partition mode is used, a CU is split evenly into twotriangle-shaped partitions, using either the diagonal split or theanti-diagonal split.

FIG. 18 shows two CU examples (1810) and (1820) of triangular partition.The CU (1810) is split from top-left corner to bottom-right corner(referred to as diagonal direction) into two triangular predictionunits, and the CU (1820) is split from top-right corner to bottom-leftcorner (referred to as inverse diagonal direction) into two triangularprediction units PU1 and PU2. Each triangular prediction unit in the CUis inter-predicted using its own uni-prediction motion vector andreference frame index which are derived from a uni-prediction candidatelist. Further, an adaptive weighting process is performed to thediagonal edge after predicting the triangular prediction units. Then,the transform and quantization process are applied to the whole CU. Itis noted that the triangular partition is only applied to skip and mergemodes.

In some examples, each triangle partition in the CU is inter-predictedusing its own motion vector; only uni-prediction is allowed for eachpartition, that is, each partition has one motion vector and onereference index. The uni-prediction motion constraint is applied toensure that same as the conventional bi-prediction, only two motioncompensated predictions are used for each CU. The uni-prediction motioninformation for each partition is derived from a uni-predictioncandidate list constructed using a process that is referred to asuni-prediction candidate list construction process.

In an example, when the CU-level flag indicates that the current CU iscoded using the triangle partition mode, an index in the range of [0,39] is further signalled. Using this triangle partition index, thedirection of the triangle partition (diagonal or anti-diagonal), as wellas the motion for each of the partitions can be obtained through alook-up table. After predicting each of the triangle partitions, thesample values along the diagonal or anti-diagonal edge are adjustedusing a blending processing with adaptive weights. The result of theblending process is the prediction signal for the whole CU, andtransform and quantization process can be applied to the whole CU as inother prediction modes. Finally, the motion field of a CU predictedusing the triangle partition mode is stored in 4×4 units.

According to an aspect of the disclosure, the unit-prediction candidatelist construction process constructs a uni-prediction candidate listthat includes five uni-prediction motion vector candidates.

FIG. 19 shows an example for forming a uni-prediction candidate list fora current block (1910). In an example, the uni-prediction candidate listconsists of five uni-prediction motion vector candidates. Theuni-prediction candidate list is derived from seven neighboring blocksincluding five spatial neighboring blocks (1 to 5 as shown in FIG. 19 )and two temporal co-located blocks (6 to 7 as shown in FIG. 19 ). Forexample, the motion vectors of the seven neighboring blocks arecollected and put into the uni-prediction candidate list in certainorder, such as uni-prediction motion vectors first. Then, for thebi-predicted neighboring blocks, the L0 motion vectors (that is, the L0motion vector part of the bi-prediction MV), the L1 motion vectors (thatis, the L1 motion vector part of the bi-prediction MV), and averagedmotion vectors of the L0 and L1 motion vectors of the bi-prediction MVsare put into the uni-prediction candidate list. When the number ofcandidates is less than five, zero motion vector is added to the end ofthe list.

In some examples, 40 possible ways can be used to predict a CU coded intriangle partition mode. The 40 possible ways are determined as 5 (forpartition 1 motion)×4 (for partition 2 motion)×2 (diagonal oranti-diagonal partition modes). The triangle partition index in therange of [0, 39] is used to identify which one of these possibilities isused using a look-up table, such as Table 3. In Table 3, triangle_idxdenotes the triangle partition index in the range of [0,39];triangle_dir denotes the direction of the partition (e.g., diagonal oranti-diagonal partition modes); part_1_cand denotes the index of theselected candidate for partition 1, part_2_cand denotes the index of theselected candidate for partition 2.

TABLE 3 Look up table to derive triangle direction and partition motionsbased on triangle index triangle_idx 0 1 2 3 4 5 6 7 8 9 10 11 12 13 1415 16 17 18 19 triangle_dir 0 1 1 0 0 1 1 1 0 0 0 0 1 0 0 0 0 1 1 1Part_ l_cand 1 0 0 0 2 0 0 1 3 4 0 1 1 0 0 1 1 1 1 2 Part_2_cand 0 1 2 10 1 4 0 0 0 2 2 2 4 3 3 4 4 3 1 triangle_idx 20 21 22 23 24 25 26 27 2829 30 31 32 33 34 35 36 37 38 39 triangle_dir 1 0 0 1 1 1 1 1 1 1 0 0 10 1 0 0 1 0 0 Part_1_cand 2 2 4 3 3 3 4 3 2 4 4 2 4 3 4 3 2 2 4 3Part_2_cand 0 1 3 0 2 4 0 1 3 1 1 3 2 2 3 1 4 4 2 4

After the predictions of the triangle partitions using respective motioninformation, blending is applied to the two prediction signals to derivesamples around the diagonal or anti-diagonal edge, as illustrated inFIG. 22 by weighted area for block (2210) and weighted area for block(2220). The blending process adaptively chooses weights depending on themotion vector difference between the two partitions.

In an example, two weighting factor groups are used. The first weightingfactor group includes {7/8, 6/8, 4/8, 2/8, 1/8} for luminance samplesand {7/8, 4/8, 1/8} for the chrominance samples, respectively. Thesecond weighting factor group includes {7/8, 6/8, 5/8, 4/8, 3/8, 2/8,1/8} for the luminance samples and {6/8, 4/8, 2/8} for the chrominancesamples, respectively.

FIG. 20 shows an example of using the first weighting factor group toderive the final prediction for a CU according to some embodiments ofthe disclosure. FIG. 20 shows weighting factors (2010) for luminancesamples and weighting factors (2020) for chrominance samples.

FIG. 21 shows an example of using the second weighting factor group toderive the final prediction for a CU according to some embodiments ofthe disclosure. FIG. 21 shows weighting factors (2110) for luminancesamples and weighting factors (2120) for chrominance samples.

The second weighting factor group has more luma weights and blends moreluma samples along the partition edge. In some examples, when thereference pictures of the two triangle partitions are different fromeach other, or when their motion vector difference is larger than 16luma samples, the second weighting factor group is selected; otherwise,the first weighting factor group is selected.

For example, for a luminance sample, P1 is the uni-prediction of PU1, P2is the uni-prediction of PU2. Using FIG. 20 as an example, when theweighting factor is shown as P1, the final prediction is solelydetermined by the uni-prediction of PU1; when the weighing factor isshown as P2, the final prediction is solely determined by theuni-prediction of PU2. When the weighing factor is shown as a number,the number is indicative of a weight for the uni-prediction of PU1. Forexample, when the weighting factor is 2, the final prediction iscalculated according to Eq. 3; when the weighting factor is 4, the finalprediction is calculated according to Eq. 3; and when the weightingfactor is 7, the final prediction is calculated according to Eq. 5:Final Prediction=2/8×P1+6/8×P2  Eq. 3Final Prediction=4/8×P1+4/8×P2  Eq. 4Final Prediction=7/8×P1+1/8×P2  Eq. 5

Combined inter and intra prediction (CIIP) is another tool that is usedin VTM3 in some examples. In VTM3, when a CU is coded in merge mode, andif the CU includes at least 64 luma samples (that is, CU width times CUheight is equal to or larger than 64), an additional flag is signaled toindicate if the combined inter/intra prediction (CIIP) mode is appliedto the current CU.

In some embodiments, in order to form the CIIP prediction, an intraprediction mode is first derived from two additional syntax elements. Upto four possible intra prediction modes can be used, such as DC, planar,horizontal, or vertical. Then, the inter prediction and intra predictionsignals are derived using regular intra and inter decoding processes.Finally, weighted averaging of the inter and intra prediction signals isperformed to obtain the CIIP prediction.

In an embodiment, up to 4 intra prediction modes, including DC, planar,horizontal, and vertical, can be used to predict the luma component inthe CIIP mode. When the CU shape is very wide (that is, width is morethan two times of height), then the horizontal mode is not allowed. Whenthe CU shape is very narrow (that is, height is more than two times ofwidth), then the vertical mode is not allowed. In such cases, 3 intraprediction modes are allowed.

In some embodiments, the CIIP mode uses 3 most probable modes (MPM) forintra prediction. The CIIP MPM candidate list can be formed as follows.

In a first step to form the CIIP MPM candidate list, in an example, theleft and top neighbouring blocks are set as A and B, respectively.

In a second step to form the CIIP MPM candidate list, the intraprediction modes of block A and block B, denoted as intraModeA andintraModeB, respectively, are derived. For example, let X be either A orB. The intraModeX is set to DC when 1) block X is not available; or 2)block X is not predicted using the CIIP mode or the intra mode; 3) blockB is outside of the current CTU. Otherwise, intraModeX is set to 1) DCor planar if the intra prediction mode of block X is DC or planar; or 2)vertical if the intra prediction mode of block X is a “vertical-like”angular mode (larger than 34), or 3) horizontal if the intra predictionmode of block X is a “horizontal-like” angular mode (smaller than orequal to 34).

In a third step, when intraModeA and intraModeB are the same, ifintraModeA is planar or DC, then the three MPMs are set to {planar, DC,vertical} in that order; otherwise, the three MPMs are set to{intraModeA, planar, DC} in that order.

In the third step, when intraModeA and intraModeB are different, thefirst two MPMs are set to {intraModeA, intraModeB} in that order. Forthe third MPM, the uniqueness of planar, DC and vertical is checked inthat order against the first two MPM candidate modes (e.g., intraModeAand intraModeB); and as soon as a unique mode is found, the unique modeis added to as the third MPM.

In some examples, the CU shape is very wide or very narrow as definedabove (one side is more than twice of the other side), the MPM flag isinferred to be 1 without signalling. Otherwise, an MPM flag is signalledto indicate if the CIIP intra prediction mode is one of the CIIP MPMcandidate modes.

When the MPM flag is 1, an MPM index is further signalled to indicatewhich one of the MPM candidate modes is used in CIIP intra prediction.Otherwise, if the MPM flag is 0, the intra prediction mode is set to the“missing” mode in the MPM candidate list. For example, if the planarmode is not in the MPM candidate list, then planar is the missing mode,and the intra prediction mode is set to planar. Since 4 possible intraprediction modes are allowed in CIIP, and the MPM candidate listcontains only 3 intra prediction modes, one of the 4 possible modes canbe determined to be the missing mode.

In an example, for the chroma components, the derived mode (DM) mode isalways applied without additional signalling; that is, chroma uses thesame prediction mode as luma.

In some examples, the intra prediction mode of a CIIP-coded CU will besaved and used in the intra mode coding of the future neighbouring CUs.

After the inter prediction signal and the intra prediction signal arederived, the inter prediction signal and the intra prediction signal arecombined. For example, the inter prediction signal in the CIIP modeP_(inter) is derived using the same inter prediction process applied toregular merge mode; and the intra prediction signal P_(intra) is derivedusing the CIIP intra prediction mode following the regular intraprediction process. Then, the intra and inter prediction signals arecombined using weighted averaging. In some examples, the weight valuedepends on the intra prediction mode and the location of the sample inthe coding block. In an example, when the intra prediction mode is theDC or planar mode, or when the block width or height is smaller than 4,then equal weights are applied to the intra prediction and the interprediction signals.

In another example, when the intra prediction mode is either horizontalmode or vertical mode, the weights are determined based on the intraprediction mode and the sample location in the block. Taking thehorizontal prediction mode for example (the weights for the verticalmode can be derived similarly but in the orthogonal direction), Wdenotes the width of the block and H denotes the height of the block.The coding block is first split into four equal-area parts, each of thedimension is (W/4)×H. Starting from the part closest to the intraprediction reference samples and ending at the part farthest away fromthe intra prediction reference samples, the weight wt for each of the 4regions is set to 6, 5, 3, and 2, respectively. The final CIIPprediction signal is derived using Eq. 6:P _(CIIP)=((8−wt)×P _(inter)+wt×P _(intra)+4)>>3  (Eq. 6)

In another example to signal triangular prediction, when triangularprediction is applied to a block, for a block located at (xCb, yCb), themerge_triangle_idx[xCb][yCb] ranging from 0 to 39 is not signaled, thenthe lookup table of Table 3 is no longer necessary. Instead, threesyntax elements, i.e., split_dir[xCb][yCb],merge_triangle_idx0[xCb][yCb] and merge_triangle_idx1[xCB][yCb], aresignaled. The syntax element split_dir[xCb][yCb] is either 0 or 1, thesyntax element merge_triangle_idx0[xCb][yCb] is 0, 1, 2, 3, or 4, andthe syntax element merge_triangle_idx1[xCb][yCb] is 0, 1, 2, or 3. Thesyntax elements merge_triangle_idx0[xCb][yCb] andmerge_triangle_idx1[xCb][yCb] can be binarized using different methods,such as truncated unary coding or truncated binary coding. Table 4 andTable 5 show examples of Truncated unary and binary coding. In addition,different context models may be applied on each bin in the binarizedvalues.

TABLE 4 Truncated unary and binary coding with maximum valid value equalto 4 (inclusive) symbol truncated unary coding truncated binary coding 00 00 1 10 01 2 110 10 3 1110 110 4 1111 111

TABLE 5 Truncated unary and binary coding with maximum valid value equalto 3 (inclusive) symbol truncated unary coding binary coding 0 0 00 1 1001 2 110 10 3 111 11

In some examples, two variables, m and n, are defined to indicate themerge candidate indices for the two prediction units in the triangularprediction, where m and n can be 0, 1, 2, 3, or 4 in any combinationexcept that m and n shall not be equal. The merge_triangle_idx[xCb][yCb]may be derived from m, n and split_dir[xCb][yCb]. Further, differentmappings can be used to map from merge_triangle_idx0[xCb][yCb] andmerge_triangle_idx1[xCb][yCb] to the actual merge candidates used by thetwo triangular partitions.

According to some aspects of the disclosure, many new inter predictionmodes, such as MMVD, SbTMVP, CIIP, triangle, affine merge, affine AMVP,and the like can be used to improve video coding from various aspects.The syntax elements for the inter prediction modes may have differentstatistical distributions under a fixed or different coding parametersettings. Signaling techniques for the inter prediction modes can bemodified to achieve a better coding efficiency.

Aspects of the disclosure provide modified signaling techniques forcertain inter-prediction modes for better coding efficiency. Theproposed methods may be used separately or combined in any order.Further, each of the methods (or embodiments), encoder, and decoder maybe implemented by processing circuitry (e.g., one or more processors orone or more integrated circuits). In one example, the one or moreprocessors execute a program that is stored in a non-transitorycomputer-readable medium. In the following, the term block may beinterpreted as a prediction block, a coding block, or a coding unit,i.e. CU. The disclosed methods modify the decoding process of a videocodec so that the parsing and interpretation of inter-prediction relatedsyntax elements are modified.

According to some aspects of the disclosure, modifications can be addedto associate some of the inter prediction modes to merge_flag beingfalse (e.g., 0) instead of merge_flag being true (e.g., 1). In someexamples, when too many inter prediction modes are associated with themerge_flag being true, the decoding of the syntax elements for the interprediction modes may take longer time (e.g., too many “if” clauses).Thus, when some of the inter prediction modes are modified to beassociated with merge_flag being false, the decoding time, which isrelated to the number of “if” clauses in some examples, can be reduced.

In some embodiments, the syntax elements of certain inter-predictiontools (for the corresponding inter prediction modes) are signaled whenmerge_flag (either signaled or implied) is false (e.g., 0). In someexamples, the certain inter-prediction tools are referred to aspseudo_non_merge_modes, and a list of the pseudo_non_merge_modes can bevirtually constructed. In some examples, the list ofpseudo_non_merge_modes includes at least one of the inter-predictiontools in MMVD, SbTMVP, CIIP, triangle, affine merge, advanced MVP(AMVP), affine AMVP, and the like. It is noted that AMVP refers to amode with signaling of the regular inter-prediction parameters,including reference index, MVD, etc. In one example, thepseudo_non_merge_modes may include MMVD and AMVP. In another example,the pseudo_non_merge_modes may include MMVD, CIIP, and affine merge.

The list of the pseudo_non_merge_modes can be constructed in variousways (e.g., using one or combinations from multiple methods as describedbelow). In some embodiments, the construction method is fixed and isused by both encoder and decoder.

In an embodiment, the pseudo_non_merge_modes includes inter predictionmodes that use MVD in prediction. In an example, when MVD is notassociated with an inter-prediction tool (e.g., triangle), theinter-prediction tool is not included in pseudo_non_merge_modes.Otherwise, the inter prediction tool is included inpseudo_non_merge_modes.

In another embodiment, AMVP is not included in thepseudo_non_merge_modes.

In another embodiment, AMVP is always included in thepseudo_non_merge_modes.

In another embodiment, when AMVP is included in thepseudo_non_merge_modes, AMVP is always the last one by order in the listof pseudo_non_merge_modes.

In another embodiment, the tools in pseudo_non_merge_modes can be in anyorder.

In another embodiment, when both affine merge and affine AMVP areincluded in pseudo_non_merge_modes, the signaling of these two modes areunified. In an example, two syntax elements (e.g., two flags) are usedtogether to indicate whether one of the affine merge and the affine AMVPis used for inter prediction of the current block. For example, a firstsyntax element is signaled to indicate whether affine prediction(including affine merge and affine AMVP) is applied. When the firstsyntax element is true (meaning affine prediction), a second syntaxelement is signaled to indicate whether the inter prediction mode isaffine merge or affine AMVP. When the inter prediction mode is affinemerge, additional syntax elements for the affine merge can be signaled(e.g., affine merge index). When the inter prediction mode is affineAMVP, additional syntax elements for the affine AMVP can be signaled(e.g., a flag indicating 4-parameter or 6-parameter affine, and thecorresponding affine parameters of affine MVP index for the block andMVD for each control point).

In some embodiments, all tools in the list of pseudo_non_merge_modes aresignaled by individual flags sequentially. In an embodiment, the lasttool in the list of pseudo_non_merge_modes is applied without additionalsignaling when other tools in pseudo_non_merge_modes are not activated(usage flags signaled or inferred as false). In an example,pseudo_non_merge_modes include MMVD, CIIP, and AMVP, and then a firstflag corresponding to MMVD and a second flag corresponding to CIIP canbe used. The first flag is signaled to indicate whether MMVD is used inthe coding block. When the first flag is true, additional MMVD syntaxelements can be signaled. When the first flag is false, the second flagis signaled to indicate whether CIIP is used in the coding block. Whenthe second flag is true, additional CIIP syntax elements are signaled.When both the first flag and the second flag are false, AMVP is usedwithout additional signaling.

In some embodiments, instead of signaling individual flags for eachtool, an index may be signaled to indicate which tool is used. When atool is used, additional syntax elements related to that tool may besignaled after the index.

In an example, when the list of pseudo_non_merge_modes includes only onetool, the index is not signaled but inferred as 0.

In another example, when the list of pseudo_non_merge_modes includes twotools, an index in [0, 1] is signaled. In an example, 0 indicates thefirst tool in the list of pseudo_non_merge_modes is used, and 1indicates the second tool in list of pseudo_non_merge_modes is used. Forexample, when the list of the pseudo_non_merge_modes include MMVD andaffine merge, then an index in [0, 1] can be signaled. When the index is0, MMVD is used, and when the index is 1, affine merge is used.

In another example, the list of pseudo_non_merge_modes includes N tools,an index in [0, 1, . . . , N−1] can be signaled. For example, when theindex is 0, the first tool is used; when the index is 1, the second toolis used; and when the index is N−1, the last tool is used. The index canbe coded using any suitable coding technique, such as truncated unarycoding, truncated binary coding, binary coding, Golomb-Rice coding, etc.

FIG. 23 shows a flow chart outlining a process (2300) according to anembodiment of the disclosure. The process (2300) can be used in thereconstruction of a block coded in intra mode, so to generate aprediction block for the block under reconstruction. In variousembodiments, the process (2300) are executed by processing circuitry,such as the processing circuitry in the terminal devices (210), (220),(230) and (240), the processing circuitry that performs functions of thevideo encoder (303), the processing circuitry that performs functions ofthe video decoder (310), the processing circuitry that performsfunctions of the video decoder (410), the processing circuitry thatperforms functions of the video encoder (503), and the like. In someembodiments, the process (2300) is implemented in software instructions,thus when the processing circuitry executes the software instructions,the processing circuitry performs the process (2300). The process startsat (S2301) and proceeds to (S2310).

At (S2310), prediction information of a current block is decoded. Theprediction information is indicative of a subset of inter predictionmodes that are associated with the merge flag being false. In somerelated examples, the subset of inter prediction modes are used to beassociated with the merge flag being true. In the present disclosure,the inter prediction modes in the subset are referred to aspseudo_non_merge_modes, and are associated with merge flag being false,in order to improve coding efficiency.

At (S2320), one or more addition flags are decoded. The additional flagsare used for selecting a specific inter prediction mode from the subsetof inter prediction modes. When the specific inter prediction mode usesadditional information for prediction, addition syntax elements aredecoded.

At (S2330), samples of the current block are reconstructed according tothe specific inter prediction mode. Then the process proceeds to (S2399)and terminates.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 24 shows a computersystem (2400) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 24 for computer system (2400) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (2400).

Computer system (2400) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (2401), mouse (2402), trackpad (2403), touchscreen (2410), data-glove (not shown), joystick (2405), microphone(2406), scanner (2407), camera (2408).

Computer system (2400) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (2410), data-glove (not shown), or joystick (2405), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (2409), headphones(not depicted)), visual output devices (such as screens (2410) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (2400) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(2420) with CD/DVD or the like media (2421), thumb-drive (2422),removable hard drive or solid state drive (2423), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (2400) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (2449) (such as, for example: USB ports of thecomputer system (2400)); others are commonly integrated into the core ofthe computer system (2400) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (2400) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (2440) of thecomputer system (2400).

The core (2440) can include one or more Central Processing Units (CPU)(2441), Graphics Processing Units (GPU) (2442), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(2443), hardware accelerators for certain tasks (2444), and so forth.These devices, along with Read-only memory (ROM) (2445), Random-accessmemory (2446), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (2447), may be connectedthrough a system bus (2448). In some computer systems, the system bus(2448) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (2448),or through a peripheral bus (2449). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (2441), GPUs (2442), FPGAs (2443), and accelerators (2444) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(2445) or RAM (2446). Transitional data can be also be stored in RAM(2446), whereas permanent data can be stored for example, in theinternal mass storage (2447). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (2441), GPU (2442), massstorage (2447), ROM (2445), RAM (2446), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (2400), and specifically the core (2440) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (2440) that are of non-transitorynature, such as core-internal mass storage (2447) or ROM (2445). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (2440). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(2440) and specifically the processors therein (including CPU, GPU, PGA,and the like) to execute particular processes or particular parts ofparticular processes described herein, including defining datastructures stored in RAM (2446) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (2444)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

-   JEM: joint exploration model-   VVC: versatile video coding-   BMS: benchmark set-   MV: Motion Vector-   HEVC: High Efficiency Video Coding-   SEI: Supplementary Enhancement Information-   VUI: Video Usability Information-   GOPs: Groups of Pictures-   TUs: Transform Units,-   PUs: Prediction Units-   CTUs: Coding Tree Units-   CTBs: Coding Tree Blocks-   PBs: Prediction Blocks-   HRD: Hypothetical Reference Decoder-   SNR: Signal Noise Ratio-   CPUs: Central Processing Units-   GPUs: Graphics Processing Units-   CRT: Cathode Ray Tube-   LCD: Liquid-Crystal Display-   OLED: Organic Light-Emitting Diode-   CD: Compact Disc-   DVD: Digital Video Disc-   ROM: Read-Only Memory-   RAM: Random Access Memory-   ASIC: Application-Specific Integrated Circuit-   PLD: Programmable Logic Device-   LAN: Local Area Network-   GSM: Global System for Mobile communications-   LTE: Long-Term Evolution-   CANBus: Controller Area Network Bus-   USB: Universal Serial Bus-   PCI: Peripheral Component Interconnect-   FPGA: Field Programmable Gate Areas-   SSD: solid-state drive-   IC: Integrated Circuit-   CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method for video encoding in an encoder,comprising: obtaining samples of a current block to be encoded by theencoder; encoding the samples of the current block according to aspecific inter prediction mode to obtain encoded data; and generating acoded video bitstream, the coded video bitstream including the encodeddata and prediction information, the prediction information including amerge flag for the current block being false and at least one syntaxelement indicating which one of inter prediction modes in a subset ofavailable inter prediction modes is selected as the specific interprediction mode, the inter prediction modes in the subset beingassociated with the merge flag for the current block being false,wherein the subset comprises two or more of a merge with motion vectordifference (MMVD) inter prediction mode, a subblock based temporalmotion vector predictor (SbTMVP) prediction mode, a combined inter andintra prediction (CIIP) inter prediction mode, a triangle interprediction mode, an affine merge inter prediction mode, an advancedmotion vector predictor (AMVP) inter prediction mode, and an affine AMVPinter prediction mode.
 2. The method of claim 1, wherein each of theinter prediction modes in the subset uses a motion vector difference inprediction.
 3. The method of claim 1, wherein the AMVP inter predictionmode is not in the subset.
 4. The method of claim 1, wherein the AMVPinter prediction mode is in the subset.
 5. The method of claim 1,wherein the specific inter prediction mode is one of the affine mergeinter prediction mode and the affine AMVP inter prediction mode, and theat least one syntax element includes a first flag indicating an affinemode, and a second flag indicating which one of the affine merge interprediction mode and the affine AMVP inter prediction mode is selected asthe specific inter prediction mode.
 6. The method of claim 1, whereinthe at least one syntax element includes multiple flags respectivelycorresponding to the inter prediction modes in the subset to select thespecific inter prediction mode.
 7. The method of claim 1, wherein the atleast one syntax element includes multiple flags respectivelycorresponding to the inter prediction modes in the subset that areordered before a last one mode in the subset, and the multiple flags areset to be false when the last one mode in the subset is selected as thespecific inter prediction mode.
 8. The method of claim 1, wherein the atleast one syntax element includes an index indicating the specific interprediction mode from the inter prediction modes in the subset.
 9. Anapparatus for video encoding, comprising: processing circuitryconfigured to: obtain samples of a current block to be encoded by theapparatus; encode the samples of the current block according to aspecific inter prediction mode to obtain encoded data; and generate acoded video bitstream, the coded video bitstream including the encodeddata and prediction information, the prediction information including amerge flag for the current block being false and at least one syntaxelement indicating which one of inter prediction modes in a subset ofavailable inter prediction modes is selected as the specific interprediction mode, the inter prediction modes in the subset beingassociated with the merge flag for the current block being false,wherein the subset comprises two or more of a merge with motion vectordifference (MMVD) inter prediction mode, a subblock based temporalmotion vector predictor (SbTMVP) prediction mode, a combined inter andintra prediction (CIIP) inter prediction mode, a triangle interprediction mode, an affine merge inter prediction mode, an advancedmotion vector predictor (AMVP) inter prediction mode, and an affine AMVPinter prediction mode.
 10. The apparatus of claim 9, wherein each of theinter prediction modes in the subset uses a motion vector difference inprediction.
 11. The apparatus of claim 9, wherein the AMVP interprediction mode is not in the subset.
 12. The apparatus of claim 9,wherein the AMVP inter prediction mode is in the subset.
 13. Theapparatus of claim 9, wherein the specific inter prediction mode is oneof the affine merge inter prediction mode and the affine AMVP interprediction mode, and the at least one syntax element includes a firstflag indicating an affine mode, and a second flag indicating which oneof the affine merge inter prediction mode and the affine AMVP interprediction mode is selected as the specific inter prediction mode. 14.The apparatus of claim 9, wherein the at least one syntax elementincludes multiple flags respectively corresponding to the interprediction modes in the subset to select the specific inter predictionmode.
 15. The apparatus of claim 9, wherein the at least one syntaxelement includes multiple flags respectively corresponding to the interprediction modes in the subset that are ordered before a last one modein the subset, and the multiple flags are set to be false when the lastone mode in the subset is selected as the specific inter predictionmode.
 16. The apparatus of claim 9, wherein the at least one syntaxelement includes an index indicating the specific inter prediction modefrom the inter prediction modes in the subset.
 17. A non-transitorycomputer-readable medium storing instructions which when executed by acomputer cause the computer to perform: obtaining samples of a currentblock to be encoded by the computer; encoding the samples of the currentblock according to a specific inter prediction mode to obtain encodeddata; and generating a coded video bitstream, the coded video bitstreamincluding the encoded data and prediction information, the predictioninformation including a merge flag for the current block being false andat least one syntax element indicating which one of inter predictionmodes in a subset of available inter prediction modes is selected as thespecific inter prediction mode, the inter prediction modes in the subsetbeing associated with the merge flag for the current block being false,wherein the subset comprises two or more of a merge with motion vectordifference (MMVD) inter prediction mode, a subblock based temporalmotion vector predictor (SbTMVP) prediction mode, a combined inter andintra prediction (CIIP) inter prediction mode, a triangle interprediction mode, an affine merge inter prediction mode, an advancedmotion vector predictor (AMVP) inter prediction mode, and an affine AMVPinter prediction mode.
 18. The non-transitory computer-readable mediumof claim 17, wherein the specific inter prediction mode is one of theaffine merge inter prediction mode and the affine AMVP inter predictionmode, and the at least one syntax element includes a first flagindicating an affine mode, and a second flag indicating which one of theaffine merge inter prediction mode and the affine AMVP inter predictionmode is selected as the specific inter prediction mode.
 19. Thenon-transitory computer-readable medium of claim 17, wherein the atleast one syntax element includes multiple flags respectivelycorresponding to the inter prediction modes in the subset to select thespecific inter prediction mode.
 20. The non-transitory computer-readablemedium of claim 17, wherein the at least one syntax element includesmultiple flags respectively corresponding to the inter prediction modesin the subset that are ordered before a last one mode in the subset, andthe multiple flags are set to be false when the last one mode in thesubset is selected as the specific inter prediction mode.